To partly remedy the inadequacy of the nonrelativistic
wave function as the momentum \(\mathbf {P}\)  increases, a
commonly used Lorentz boost factor \(\gamma _f\)  is introduced into the
decay amplitudes [1]}, [2]}, [3]}, [4]}
\(\mathcal {M}(\mathbf {P})\rightarrow \gamma _f \mathcal {M}(\gamma _f \mathbf {P}),\) 
